1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a method for repairing white defect of liquid crystal display panel.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal display panel and a backlight module. The operative principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and the liquid crystal molecules are controlled to change direction by applying electricity to a circuit of the glass substrates in order to refract out light emitting from the backlight module for generating images.
Referring to FIG. 1, the liquid crystal display panel generally comprises: a TFT (Thin-Film Transistor) substrate 100, a CF (Color Filter) substrate 300 laminated on the TFT substrate 100, and liquid crystal 500 interposed between the TFT substrate 100 and the CF substrate 300. The TFT substrate 100 generally comprises a substrate 102 and a TFT array 104 formed on the substrate 102. The TFT array 104 is formed on the substrate 102 through mask processes. During the fabrication process of the TFT array 104, pixels are often easily contaminated in the fabrication process or damaged by static electricity so as to generate line defects and pixel defects. The line defect is breaking of a signal line and pixel defect is a defect occurring in a subpixel due to abnormal shorting or open circuit of thin-film transistors.
Pixel defects are classified as white defects, dark defects, and dull defects. The white defects keeps brightening when the screen is all dark and are thus very easily noticed due to extreme sensitivity of human eyes to them. It is preferred that the white defects can be repaired to be dark defects that are always dark or at least repairing the white defects to be dull defects that are dull.
Referring to FIGS. 2 and 3, a conventional white defect repairing method applied welding through single spot shot of laser beam at an overlapping site between an ITO layer 142 and a COM layer 146. The high temperature of the laser beam melts the metals so as to electrically connect the ITO layer 142, a second metal (metal 2) layer 144, and a common wiring (COM) layer 146 to each other thereby converting a white defect into a dark defect to complete the repairing of the white defect.
However, for the conventional single spot shot welding, if the welding spot 700 is relatively small, the repairing may fail. If the welding spot 700 is relatively large and the contact area of the welding spot 700 is S1=2πr1t1 (in which r1 is the radius of the welding spot and t1 is the length of the welding spot) that is relatively large, then the contact resistance (contact resistance being inversely proportional to the contact area and the formula is R=ρL/S, in which ρ is electrical resistivity, L is thickness, and S is contact area) of the welding spot 700 is relatively small, making the repairing quality deteriorating.